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Structures of the I-, II- and H-Methane Clathrates and the Ice−Methane Clathrate Phase Transition from Quantum-Chemical Modeling with Force-Field Thermal Corrections
Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.ORCID iD: 0000-0002-5341-2637
2011 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 23, 6169-6176 p.Article in journal (Refereed) Published
Abstract [en]

Methane hydrates with the three clathrate structures I, II and H are studied by quantumchemicalmethods. The periodic B3LYP computations are combined with force-field methodsfor the thermal energy corrections. The pressure dependencies for the crystal structures, latticeenergies and guest molecule interactions are derived. Quantum-chemical geometryoptimizations predict too small cell volumes compared to experimental data, but includingzero-point energy and thermal energy the cell volume increases and the correct densities areobtained. Phase diagram for the three structures are investigated, and phase transitions werefound at 5 GPa for the MH-I–MH-II transition and at 10 GPa for the MH-II–MH-H transition.

Place, publisher, year, edition, pages
ACS Publications , 2011. Vol. 115, no 23, 6169-6176 p.
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-53177DOI: 10.1021/jp111328vOAI: diva2:287416
The original title of this article was: "Structure and phase transitions of I-, II- and H- methane clathrates and ice from quantum-chemical B3LYP computations with corrections for thermal effects".Available from: 2010-01-18 Created: 2010-01-18 Last updated: 2015-03-09Bibliographically approved
In thesis
1. Theoretical Investigations of Water Clusters, Ice Clathrates and Functionalized Nanoparticles
Open this publication in new window or tab >>Theoretical Investigations of Water Clusters, Ice Clathrates and Functionalized Nanoparticles
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanosized structures are of intermediate size between individual molecules and bulkmaterials which gives them several unique properties. At the same time their relative limitedsizes make them suitable for studies by the methods of computational chemistry. In this thesiswater clusters, ice clathrates and functionalized metal-oxide nanoparticles have been studiedby quantum-chemical calculations and statistical thermodynamics.

The stabilities of water clusters composed of up to 100 molecules have been investigated. Themultitude of possible H-bonded topologies and their importance for determining theproperties of the clusters have been highlighted. Several structural characteristics of thehydrogen bonded network have been examined and the structural factors that determine thestability of an H-bonded network have been identified. The stability of two kinds of oxygenframeworks for water clusters have been analyzed, taking into account thermal energy andentropy corrections. Clusters with many 4-coordinated molecules have been found to be lowerin energy at low temperatures whereas the clusters with less-coordinated molecules dominateat higher temperatures. The equilibrium size distribution of water clusters as a function oftemperature and pressure has been computed using statistical thermodynamics. Themicroscopic local structure of liquid water has been probed by utilizing information from thestudied water clusters. The average number of H-bonds in liquid water has been predicted byfitting calculated average IR spectra for different coordination types in water clusters toexperimental IR spectra.

Water can form an ice-like structure that encloses various molecules such as methane. Thesemethane hydrates are found naturally at the ocean floor and in permafrost regions and canconstitute a large unemployed energy resource as well as a source of an effective green-housegas. The pressure dependencies of the crystal structures, lattice energies and phase transitionsfor the three methane hydrates with the clathrate structures I, II and H have been mapped out.

Zinc oxide is a semiconducting material with interesting luminescence properties that can beutilized in optical devices, such as photodetectors, light emitting devices and biomarkers. Theeffect of water molecules adsorbed on the ZnO surface when adsorbing organic acids havebeen investigated. Changes in optical properties by the adsorption of carboxylic acids havebeen studied and compared with experimental results. Aromatic alcohols at TiO2 metal-oxidenanoparticles have been studied as model systems for dye-sensitizied solar cells. Adsorptiongeometries are predicted and the influence from the adsorbed molecules on the electronicproperties has been studied.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 52 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1254
National Category
Other Basic Medicine
urn:nbn:se:liu:diva-52746 (URN)978-91-7393-636-1 (ISBN)
Public defence
2009-06-09, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Available from: 2010-01-18 Created: 2010-01-12 Last updated: 2015-03-09Bibliographically approved

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Lenz, AnnikaOjamäe, Lars
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